SOC Playbook: Phishing Email Investigation and Response

Phishing remains one of the most prevalent and damaging cyber threats facing organisations today. As attackers continually evolve their tactics, the need for a robust and systematic approach to phishing email investigation and response becomes paramount. This SOC playbook outlines a structured methodology for identifying, investigating, and responding to phishing email incidents, ensuring that organisations can mitigate risks and protect sensitive information effectively.

Introduction — What incident does this playbook address?

This playbook addresses the systematic investigation and response to phishing email campaigns, which are designed to deceive users into divulging sensitive information or installing malware. Phishing emails often serve as the initial access vector for attackers, leading to credential access and data collection. Given the high severity of such incidents, it is crucial for Security Operations Centres (SOCs) to have a well-defined process for managing these threats.

Detection & Triage — Initial indicators and severity assessment

Initial Indicators

The detection of a phishing email can stem from various sources, including:

• User Reports: Employees reporting suspicious emails.
• Email Filtering Systems: Security solutions flagging potential phishing attempts.
• Threat Intelligence Feeds: Alerts from external sources about ongoing phishing campaigns.

Severity Assessment

Upon detection, the SOC team should assess the severity of the incident based on the following criteria:

• Sender Reputation: Is the sender's domain known for phishing?
• Email Content: Does the email contain suspicious links or attachments?
• Targeted Users: Are high-privilege accounts or sensitive roles targeted?
• User Interaction: Has the user clicked on links or provided credentials?

A phishing email that meets multiple high-risk criteria should be classified as a high-severity incident, warranting immediate investigation.

Investigation Steps — Detailed analysis procedure

Step 1: Email Header Analysis

Begin by extracting and analysing the email headers to identify the true sender's IP address and the path taken by the email. Look for discrepancies between the "From" address and the actual sender.

Step 2: URL Inspection

Inspect any links within the email. Use URL scanning tools (e.g., VirusTotal) to check for known malicious links. If the URL redirects to a legitimate-looking site, investigate further to determine if it has been compromised.

Step 3: Attachment Analysis

If the email contains attachments, perform a static analysis using antivirus solutions and a dynamic analysis in a controlled environment (sandbox). This helps identify potential malware.

Step 4: User Interaction Verification

Confirm whether the targeted user has interacted with the phishing email. Check for:

• Credential submissions on suspicious sites.
• Malware installations on their device.

Step 5: Contextual Investigation

Gather context around the incident by reviewing logs from email gateways, user activity logs, and network traffic. This can help identify the extent of the attack and whether lateral movement has occurred within the organisation.

Containment & Eradication — How to stop and remove the threat

Containment

1. Email Quarantine: Immediately quarantine the phishing email across all mailboxes to prevent further user interaction.
2. User Notification: Inform the affected user(s) about the phishing attempt, advising them not to click any links or open attachments.

Eradication

1. Block Malicious URLs: Update web filtering rules to block access to any identified malicious URLs.
2. Remove Malware: If malware was installed, initiate an incident response protocol to remove it from affected systems. This may include reimaging devices or restoring from backups.
3. Credential Reset: Force a password reset for any accounts that may have been compromised to mitigate risks associated with credential access.

Recovery — Restoring normal operations

1. System Restoration: After ensuring that the threat has been eradicated, restore any affected systems to normal operation. This may involve restoring data from backups or rebuilding compromised systems.
2. User Training: Conduct training sessions to educate users on identifying phishing attempts and the importance of reporting suspicious emails.
3. Monitoring: Increase monitoring of network traffic and user activity for a period following the incident to detect any signs of residual threats or further attacks.

Lessons Learned — Post-incident improvements and reporting

After the incident has been resolved, conduct a thorough review of the response process. This should include:

• Incident Report: Document the timeline of events, actions taken, and outcomes. This report should be shared with relevant stakeholders to enhance awareness.
• Process Improvement: Identify any gaps in the detection, investigation, or response phases and implement improvements. This may involve updating playbooks, enhancing training programmes, or investing in more sophisticated email security solutions.
• Threat Intelligence Sharing: Contribute findings to threat intelligence platforms to help other organisations defend against similar phishing campaigns.

In conclusion, a well-defined SOC playbook for phishing email investigation and response is essential for minimising risks associated with these high-severity incidents. By following a structured approach, organisations can enhance their email security posture, reduce the likelihood of successful attacks, and improve overall incident response capabilities.

For tailored assistance in developing and implementing effective cybersecurity strategies, contact CyberZonic today. Our team of experts is ready to help you fortify your organisation against phishing and other cyber threats.